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Random no more: Evolution isn’t down to chance alone

Arginine dream&colon; how do amino acids turn into superstar proteins? (Image&colon; David Parker/SPL)

Where do evolution’s adaptations come from? Arrival of the fittest by Andreas Wagner has some surprising answers

EVOLUTION, we have always been told, results from natural selection sifting through countless random variations over millions of years.

That’s not good enough, says Andreas Wagner, a systems biologist at the University of Zurich in Switzerland. Natural selection can explain which adaptations survive over time, he argues, but it falls far short of explaining where those adaptations originate.

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For over a decade, Wagner has been looking for an answer that would satisfy him, and Arrival of the Fittest presents his research to a general audience for the first time. In it, he makes a persuasive case that the origin of adaptations – the arrival of the fittest, rather than the survival of the fittest – can’t be down to pure chance alone.

Imagine a vast library, one so big that it contains every possible sequence of letters. Most of the books are gibberish, filled with words like “erwtvaiwq” or “avbqse”, but you can also find Hamlet and On the Origin of Species. This is the book’s core metaphor, used, for example, to describe how most strings of amino acids make non-functional proteins – Wagner’s gibberish – but some make working enzymes and a few make brilliant ones.

The problem is that the library is so vast (there are more than 10130 different proteins made from just 100 amino acids) that the odds of evolution stumbling across the specific “book” it needs – an enzyme that can disarm a synthetic toxin, for example – are practically zero. Something else must guide evolution through the library.

Something must guide evolution through the library of possible proteins that the body can make

Part of the secret, Wagner tells us, is that many different proteins can perform the same function, just as many different books can tell the same story in different words. That is, instead of looking for a single meaningful book in the entire library, evolution is looking for any one of many functionally equivalent ones.

That’s not all&colon; the structure of the library makes it easy for evolution to move from one meaningful book to another. When Wagner and his colleagues tried browsing adjacent “books” – proteins that differ by a single amino acid – they found that most worked just as well as the original. The same was true when they changed another amino acid, and another. In fact, you could move, step by step, from one end of the library to the other without changing the meaning.

This allows populations to accumulate a lot of genetic variation while still remaining viable. In Wagner’s metaphor, readers spread into many different rooms of the library. And that’s where the big pay-off comes. By wandering far afield, you come to rooms with very different sorts of books nearby. In real terms, you end up in places where changing just a few more amino acids gives you a protein with a radically different function – an evolutionary breakthrough, close at hand.

And the more hidden variation the population accumulates, the more likely that this will happen. As Wagner puts it, “while you walk along one of these trails, the innovation you are searching for will appear at some point in a small neighborhood near you”. That’s a big claim, and a far cry from pure, random chance.

In other chapters, Wagner shows that the same principle holds for networks of metabolic and regulatory genes. Indeed, these linked pathways through diverse libraries may turn up in any sufficiently complex system, he says. In what may be the least convincing part of the book, he even speculates that we may be able to apply these principles to algorithms, letting artificial intelligence innovate faster than human inventors ever could.

Whatever the likelihood of that, Wagner’s book is an eye-opener. As a bonus, his writing is clear and elegant, with vivid analogies and concrete examples to illustrate his key points. You’ll never think about evolution in the same way again.